The field of the invention is ceramic bodies which have one or more of nitride phases of Al and/or Si plus one or more of phases of boride, carbide, silicide and/or sulfide of Groups 3b, 4b, 5b and 6b elements. A combination of the latter compounds can be either two discrete phases (e.g. a boride and a carbide) or a single complex phase (e.g. a borocarbide).
Most commonly heretofore, these ceramic bodies have been of the type physically formed of ingredients corresponding to the crystalline phases in the ceramic bodies. By way of exemplary illustration, reference is made to the following prior art documents. U.S. Pat. No. 3,108,887 discloses hot pressed particulate mixtures of AlN with other compounds, among which are mentioned the compounds MX where M is different from X and is selected from aluminum, boron, silicon, rare earth metals, titanium, zirconium, hafnium, thorium, vanadium, columbium (niobium), tantalum, protactinium, chromium, molybdenum, tungsten and uranium (although no example is given of any of these MX compounds). U.K. Patent Specification No. 954,272 discloses bodies, either sintered or hot pressed, of particulate mixtures of AlN with a boride of titanium, zirconium, chromium or molybdenum. U.S. Pat. Nos. 3,251,700 and 3,328,280 disclose hot pressed or sintered particulate mixtures of TiB.sub.2 and AlN.
Generally those hot pressed or sintered physical mixtures require heating to relatively high temperatures of 1800.degree.-2000.degree. C. or so. Moreover, such ceramic bodies have properties which are dependent upon and limited by the inherent effects of the physical nature of their ingredients which are physically combined. The distribution and sizing of the phases are generally directly related to the particle sizing and mixing of ingredient powders. The powders are not always easily available in uniformly fine sizes for obtaining homogeneous distribution of phases and superior properties. Milling of powders to improve their sizing can lead to undesirable situations. In fact, some powders such as TiB.sub.2 in sizes of about 5 .mu.m or finer present fire and explosion hazard during milling due to their rapid reaction with oxygen in air under conditions of frictional heating.
Amongst numerous reactions for forming other types of multiphase bodies by an unusual reaction hot pressing process involving passage of electric current through the reaction mixture during the process, U.S. Pat. No. 3,143,413 discloses reaction hot pressed ceramics with phases of ZrN and either ThS, VaC or ZrC, but no details are given about the properties of such bodies made from -60 mesh reactant powders heated up to 1800.degree.-2300.degree. C.
There has been a continuing need for multiphase ceramics with easily controlled and predictable composition, crystal structure (including uniform phase distribution and fine grain size) and related physical properties, and which can be easily and economically fabricated in a variety of shapes by heating at lower temperatures.